1. Field of the Invention
The present invention relates to an image compression and expansion apparatus for recording image data obtained by reducing the number of pixels of an original still image on to a recording medium and later reading the image data from the recording medium and restoring the original image.
2. Description of the Related Art
In the past, as an example of image compression processing in an image compression and expansion apparatus, it has been known to find an average value of a predetermined number of pixel values included in the large number of pixels forming an original image, to generate a single pixel and to record a reduced image comprised of such pixels on to a recording medium. Further, in the image expansion processing in the image compression and expansion apparatus, the reduced image read from the recording medium is subject to interpolation so as to generate an enlarged image of the same number of pixels as the original image.
On the other hand, another image compression and expansion apparatus is known to record DCT coefficients obtained by application of a two dimensional discrete cosine transformation to a reduced image on to a recording medium and apply a two dimensional inverse discrete cosine transformation to the DCT coefficients read from the recording medium to obtain IDCT coefficients. The IDCT coefficients correspond to part of the pixels contained in the pixels of the original image. By applying interpolation to the IDCT coefficients, it is possible to generate an enlarged image of the same number of pixels as the original image.
The enlarged image reproduced by an image compression and expansion apparatus should ideally match the original image, but since part of the information included in the original image is lost at the time of generating the reduced image, normally the original image is not matched and the quality of the image becomes relatively poor.